Linux,  Uncategorized

Clamav is great

Like a lot of people, I use the free anti-virus program Clamav on my mail server. Last week, I was seriously impressed with its performance.

It started last wednesday, 25 July. At about noon, I received a mail by amavisd-new that it had blocked an e-mail containing a virus, Trojan.Downloader-11827. What was strange, is that I received this message on an e-mail account which is protected by my ISPs proprietary anti-virus solution. So it had not caught this virus, while Clamav did. Then I submitted the file to, and apparently only a few (about five) anti-virus programs detected the virus. Amongst others, Kaspersky, F-Secure, NOD32, Bitdefender, Symantec and of course Clamav. In the clamav-virusdb mailing list archives, I found that Clamav had detection for this virus since 7h21 CEST, so it was really amongs the first to detect this virus.

Then friday evening, I was looking at the blocked spam messages (I use spamassassin too on this server), and noticed that it had blocked an e-mail message containing an exe file. A spam message with an exe file, that sounded suspicious, but Clamav could not detect a virus. Again I submitted the file to virustotal, and there was one positive result: Ikarus detected it as a trojan horse. I submitted the file via clamav’s website at around 19h CEST. About half an hour later, I received a message that detection for this virus had been added. I updated Clamav, and indeed, it was recognized. I checked the file again on virustotal, around 20h, and then there were 4 anti-virus programs recognizing it: Clamav, F-Prot Ikarus and Virusbuster. 1.5h later, Antivir, AVG and Kaspersky had also added detection. Other well-known anti-virus vendors, still did not detect it at that moment such as Bitdefender, F-Secure, NOD32, Panda, Sophos and Symantec.

In the meantime, F-Secure blogged about these two virus outbreaks: and

Two conclusions:

  • Clamav has an excellent response time, which is comparable to the best proprietary anti-virus solutions. If you have an e-mail server, you definitely want to integrate Clamav in it, even if you already have a proprietary solution (Clamav is particulary good in detecting phishing mails too!)
  • No anti-virus program is perfect. If you receive an e-mail message at the start of a virus outbreak, it’s quite possible that your anti-virus solution will not detect it yet, no matter which anti-virus you have.